According to The Queen Of Indexing – Kimberly Tripp – what she looks for in a clustered index is primarily: Unique Narrow Static And if you can also guarantee: Ever-increasing pattern then you’re pretty close to having your ideal clustering key! Check out her entire blog post here, and another really interesting one about clustering … Read more
According to Clustered and Secondary Indexes, you can have only one clustered index per table. All indexes other than the clustered index are known as secondary indexes. If a table has no primary index but another unique index, this is used as the clustered index. If you do not define a PRIMARY KEY for your … Read more
Note that PostgreSQL uses the term “clustered index” to use something vaguely similar and yet very different to SQL Server. If a particular index has been nominated as the clustering index for a table, then psql’s \d command will indicate the clustered index, e.g., Indexes: “timezone_description_pkey” PRIMARY KEY, btree (timezone) CLUSTER PostgreSQL does not nominate … Read more
A clustered index on GUID is not a good design. The very nature of GUID is that it’s random, while a clustered index physically orders the records by the key. The two things are completely at odds. For every insert SQL has to reorder the records on disk! Remove clustering from this index! The time … Read more
They don’t have to be unique but it certainly is encouraged. I haven’t encountered a scenario yet where I wanted to create a CI on a non-unique column. What happens if you create a CI on a non-unique column If the clustered index is not a unique index, SQL Server makes any duplicate keys unique … Read more
Clustered Index Only one per table Faster to read than non clustered as data is physically stored in index order Non Clustered Index Can be used many times per table Quicker for insert and update operations than a clustered index Both types of index will improve performance when select data with fields that use the … Read more
With a clustered index the rows are stored physically on the disk in the same order as the index. Therefore, there can be only one clustered index. With a non clustered index there is a second list that has pointers to the physical rows. You can have many non clustered indices, although each new index … Read more
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